In recent years, a short distance radio interface called Bluetooth has been developed in which a 2.45 GHz Industrial Scientific Medical (ISM) band is used as a carrier wave frequency, and various mobile apparatuses such as cellular phones, notebook-size personal computers, digital still cameras, and mobile game machines can be connected by radio.
In a radio communication system including such an interface, the same information is repeatedly transmitted in the same frequency band in some cases. When the cellular phone is used as a mobile radio apparatus, the cellular phone is constantly waiting for reception. Even when information has the same content as that of the already received information, the information is repeatedly received. Therefore, there is a problem that power consumption during reception increases and a battery is remarkably consumed. For example, while a user waits for someone in front of a station ticket gate, a train timetable, a fare table, and the like are repeatedly transmitted, such information is repeatedly received by a mobile terminal, and power is consumed during waiting. To prevent this problem, the user has to temporarily turn off a power supply of radio communication. However, with the cellular phone, when the power supply is turned off, an inherent function of the cellular phone is hindered. Therefore, this is not a realistic solution.
Moreover, since the same information is repeatedly transmitted, the radio terminal has no memory for storing the received information. Therefore, the already received portion of information cannot be confirmed. When a video/music program is transmitted in real time, and if the user starts browsing the information from a midway timing of the program, a first part of the program cannot be seen until the next transmission of the program.
On the other hand, a technique associated with power saving of the radio apparatus is disclosed in Japanese Patent Disclosure (KOKAI) No. 10-32504. This discloses a technique of judging an influence of noise or the like in an early stage, preventing a received current from increasing, and realizing the power saving. That is, if a time for which reception strength indicates a determined value or a smaller value continues for not less than a predetermined time, it can be determined that a received signal includes a noise and therefore a normal signal cannot be received. Thus, the reception is stopped. In this method, however, the same repeatedly transmitted information cannot be prevented from being received many times.
As described above, in the radio communication system using the conventional short distance radio interface, when the radio communication is performed in the same frequency band, a receiving apparatus constantly receives transmitted information. Therefore, even if the same information is received, the power consumption during reception increases, and the battery is remarkably consumed.
Moreover, when video or sound information is received in real time, the memory for storing the information being received is not provided. The information is browsed from halfway depending upon a browsing start timing. Therefore, it cannot be guaranteed that the information is transmitted to the user from the beginning.